Apparatus for marking a substrate using ionized gas

ABSTRACT

An apparatus suitable for marking a substrate comprises a holder for holding a substrate and a ground for electrically grounding the substrate. At least one needle electrode has a tip located proximate to the substrate so that there is a gap between the substrate and the tip. A high voltage source provides a current to the electrode tip to ionize the gas in the gap so that the ionized gas can impinge upon and mark the substrate.

BACKGROUND

The present invention relates to an apparatus and method for producingmarks, such as reference marks, on substrates.

Reference marks are applied on semiconductor substrates to allow precisepositioning of the substrate in fabrication and inspection processes. Inone inspection method, a light scattering surface inspection system isused to locate contaminant particles on the surface of the wafer. Thecontaminant particles are then assigned coordinates based on a referencegrid which is established using the reference marks on the wafer. Thewafer is then placed in a scanning electron microscope ("SEM"), and thereference marks on the wafer used to locate the coordinates of thecontaminant particles on the wafer.

In such inspection processes, the reference marks on the wafer must besmall. Small marks allow faster location of the coordinates for thecontaminant particles in the SEM. Without fine marks, it takes aninordinate amount of time to locate the contaminant particles on thewafer. To be effective, the reference marks should be sized smaller thanabout 100 microns, and preferably sized from about 1 micron to about 60microns.

It is difficult to create such fine reference marks. Mechanicalscratching processes that use a sharp needle to scratch the surface ofthe wafer cause unacceptably large marks, which can increase thepossibility of cracking the thin wafers. Typical laser etching processeshave coarse optic systems that produce marks having sizes greater thanabout 100 microns, and laser etching processes with fine optic systemsare expensive.

Further, current wafer marking processes often damage the region of thewafer surrounding the mark. For example, laser etching can "burn" theregion surrounding the mark. Existing processes can also createcontaminants that subsequently deposit on the regions of the wafer thatsurround the reference mark. These contaminants substantially decreasethe yield of integrated circuit chips formed from the semiconductorwafer.

Thus, it is desirable to have a marking apparatus and process that canproduce fine reference marks on substrates, without cracking thesubstrate, without damaging the surrounding regions, and withoutdepositing contaminant particles on the substrate.

SUMMARY

The present apparatus and method satisfy these needs. An apparatussuitable for practicing the present invention comprises a holder forholding a substrate and a ground for electrically grounding thesubstrate. At least one needle electrode has a tip proximate to andspaced apart from the holder, so that when a substrate is held by theholder, the electrode tip and the substrate define a gap therebetween. Ahigh voltage source provides a current to the electrode tip to ionizethe gas in the gap so that the ionized gas can impinge upon and mark thesubstrate.

The ground can contact and electrically ground the holder.Alternatively, the ground can comprise an electrically grounded pin thatcan contact and ground the substrate, through a hole in the substrateholder.

Preferably, the marking apparatus further comprises a gas deliverysystem to provide gas to the gap at a sufficiently high pressure to blowaway contaminants formed by the marking process.

A process for marking a substrate comprises the steps of: (a) placingthe tip of at least one needle electrode proximate to a substrate, sothat there is a gap between the electrode tip and the substrate, the gaphaving a gas therein; (b) electrically biasing the electrode withrespect to the substrate, preferably electrically grounding thesubstrate and applying a high voltage to the electrode; and (c) passinga current having a sufficiently high voltage through the electrode tipto ionize the gas in the gap so that the ionized gas impinges upon andmarks the substrate.

DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood from the following drawings,description and claims, where:

FIG. 1a shows a schematic of a marking apparatus of the presentinvention;

FIG. 1b shows a schematic of another version of the marking apparatus ofFIG. 1a; and

FIG. 2 shows a substrate that is marked using the apparatus of FIG. 1.

DESCRIPTION

The present invention provides an apparatus and process for markingsubstrates, such as semiconducting wafers. With reference to FIG. 1a,the apparatus 10 comprises a holder 12 for holding a substrate 14 and aground 15 for electrically grounding the substrate. At least one needleelectrode 16 has a tip 18 located proximate to and spaced apart from thesubstrate 14, so that when a substrate 14 is held by the holder 12, theelectrode tip 18 and the substrate 14 define a gap 20 therebetween. Ahigh voltage source 24 provides a high voltage current to the electrodetip 18 for ionizing the gas in the gap 20 so that the ionized gas canimpinge upon and mark the substrate 14.

The electrical ground 15 can contact the holder 12 so that the holder 12is electrically grounded. Alternatively, the ground 15 can comprise anelectrically grounded pin 26 that contacts the substrate 14 adjacent tothe needle electrode tip 18. The pin 26 can contact the substrate 14 viaa hole 28 within the holder 12, as shown in FIG. 1b, which allowselectrons from the ionized gas to flow through the substrate 14 and tothe grounded pin 26.

The apparatus 10 can comprise a single needle electrode 16 for producinga single reference mark at a time, or can comprise a plurality of needleelectrodes 16 so that multiple marks can simultaneously be formed on thesubstrate 14. The multiple electrode apparatus can further comprise aplurality of electrically grounded pins 26, each of the pins 26contacting the substrate 14 adjacent to an electrode tip 18.

The gas in the gap 20 can be an ambient gas that is present in the gap,such as air, or gas can be delivered to the gap via a gas deliverysystem 40. Preferably, the gas delivery system 40 comprises a gas source42 providing gas to a nozzle 44 that directs the gas to the gap 20 at asufficiently high pressure to blow away contaminants formed by themarking process.

The gas can be a nonreactive or inert gas such as Ar, Xe, or He. Xe ispreferred because the large Xe molecule is more effective in sputteringand marking the substrate. The gas can also be a reactive gas such asO₂, O₃, F₂, Cl₂, Br_(2l) , BCl₃, SF₆, CF₄, or C₂ F₆, which can etch thesubstrate.

When a pressurized gas is introduced into the gap 20 via the nozzle 44,the gas is typically flowed at a volumetric flow rate of from about 10sccm to about 10,000 sccm, and more typically flowed at a rate of fromabout 100 sccm to about 5,000 sccm.

To mark the substrate 14, the substrate 14 is placed in the holder 12and grounded by the electrical ground 15. Current provided by the highvoltage source 24 is passed through the electrode tip 18. The currentionizes the gas in the gap 20 so that the ionized gas impinges upon andmarks the grounded substrate 14. The substrate 14 is sputtered or etcheduntil a mark forms on the substrate. Typically, the substrate issputtered or etched for at least about 5 seconds.

The electrode voltage necessary to ionize the gas in the gap 20 dependsupon the size of the gap 20 and the type of gas. As the size of the gap20 increases or as the ionization potential of the gas increases, thevoltage necessary to ionize the gas increases. Preferably, the width ofthe gap 20 between the electrode tip 18 and the substrate 14 is lessthan about 100 millimeters, more preferably the width is less than about10 millimeters, and most preferably the width is from about 1 to about 6millimeters. For such gap distances, the voltage is typically from about1000 volts to about 10,000 volts, and more typically from about 2000volts to about 6000 volts.

Typically, a direct current from about 1 microamp to about 50 microampsis used, and more typically the current is from about 1 microamp toabout 10 microamps. The current can be also be pulsed at a frequency ofabout 10 Hz.

Preferably, the substrate 14 is marked with a plurality of symmetricallypositioned marks 50 as shown in FIG. 2. The symmetrical reference marksallow precise alignment of the substrate 14 in processing and inspectingapparatus.

EXAMPLE 1

A silicon wafer 14, having a thickness of about 0.73 mm and a diameterof about 200 mm (8 inches), was placed in a holder 12 that waselectrically grounded by the ground 15. The needle electrode tip 18 waspositioned at the center of the wafer, and the high voltage source 24was set to provide a voltage of 2000 volts to the electrode 16. The highvoltage source 24 provided a DC current of about 5 microamps that waspulsed at a frequency of 10 Hz.

The gas in the gap 20 was ambient air. The gap 20 was graduallydecreased by moving the electrode tip 18 toward the substrate 14, untilthe air in the gap 20 ionized at a gap distance of about 3 millimeters.A mark 50 was sputtered on the substrate 14 in about 5 seconds.

The mark 50 formed on the wafer 14 was determined by SEM examination tobe circular in shape with a diameter ranging from about 1 to about 5microns. There was no visible damage to the wafer in regions adjacent tothe mark 50.

EXAMPLE 2

A silicon wafer 14 similar to the wafer described above, was placed in aholder 12 having a hole 28 therethrough. The needle electrode tip 18 waspositioned above the hole 28, and a grounded pin 26 was inserted throughthe hole 28 and contacted with the wafer 14 at a region adjacent to theelectrode tip 18. The high voltage source 24 was set to provide a 10 Hzpulsed voltage of 5000 volts, with a current ranging from about 3 toabout 7 microamps.

Ambient air provided the gas in the gap 20. The gap 20 was graduallydecreased, until at about 3 millimeters, the air within the gap ionizedand sputtered the substrate 14. After about 5 seconds a mark 50 wassputtered on the substrate 14. The mark 50 was determined by SEMexamination to be circular in shape with a diameter ranging from about 1to about 5 microns. No damage was visible in adjacent regions.

The present invention has been described in considerable detail withreference to certain preferred versions thereof, however, other versionsare possible. For instance, the holder may be held at a DC potentialother than zero and still effectively act as a ground. Indeed, it ispossible to ground the electrode and apply the high voltage to theholder or wafer. Further, more complex electrical waveforms may beapplied between the wafer and the electrode as long as the gas isionized to promote the sputtering of marks into the wafer. Therefore,the spirit and scope of the appended claims should not be limited to thedescription of the preferred versions contained herein.

What is claimed is:
 1. An apparatus for marking a substrate, theapparatus comprising:(a) a holder for holding a substrate; (b) a groundfor electrically grounding the substrate; (c ) at least one needleelectrode having a tip located proximate to and spaced apart from theholder, so that when a substrate is held by the holder, the electrodetip and the substrate define a gap therebetween; and (d) a high voltagesource for providing a current to the electrode tip for ionizing the gasin the gap so that the ionized gas can impinge upon and mark thesubstrate, substantially without depositing material on the substrate.2. The apparatus of claim 1, wherein the ground contacts andelectrically grounds the holder.
 3. The apparatus of claim 1, whereinthe holder has a hole therethrough, and wherein the ground comprises anelectrically grounded pin that can contact the substrate through thehole in the holder.
 4. The apparatus of claim 1, comprising a pluralityof the needle electrodes for simultaneously forming multiple marks onthe substrate.
 5. The apparatus of claim 1, further comprising a gasdelivery system for providing gas to the gap.
 6. The apparatus of claim5, wherein the gas delivery system can provide gas at a sufficientlyhigh pressure to blow away contaminants formed by the marking process.7. The apparatus of claim 6, wherein the gas delivery system comprises anozzle that directs the gas into the gap.
 8. The apparatus of claim 1,wherein the gap has a width of less than about 100 millimeters.
 9. Theapparatus of claim 8, wherein the gap has a width of less than about 10millimeters.
 10. The apparatus of claim 1, wherein the high voltagesource can provide a voltage of from about 1000 volts to about 10,000volts.
 11. The apparatus of claim 10, wherein the high voltage sourcecan provide a voltage of from about 2000 volts to about 6000 volts. 12.The apparatus of claim 10, wherein the high voltage source can provide acurrent of from about 1 microamp to about 50 microamps.
 13. Theapparatus of claim 12, wherein the high voltage source provides acurrent of from about 1 microamp to about 10 microamps.
 14. Theapparatus of claim 1, wherein the ionized gas impinges upon and marksthe substrate by sputtering or etching the substrate.
 15. The apparatusof claim 1, wherein the gap has a width of from about 1 to about 100 mm.